jQuery(".sortable").sortable is not a function

Hi – my WordPress Widgets Page is not working – I cant see any sidebars on the rhs, and I cant drag any widgets or use screen options either – when i check in Firebug I get the following error – but i dont know how to fix the issue in wordpress (I use Thesis btw):

jQuery(".sortable").sortable is not a function
(?)()thesis...r=3.1.1 (line 192)
toArray(j=function())load-s...d1c6ac7 (line 26)
j = function()
init(j=function(), s=undefined)load-s...d1c6ac7 (line 25)
c(j=function(), s=undefined)load-s...d1c6ac7 (line 22)
(?)()thesis...r=3.1.1 (line 191)
noConflict(j=function())load-s...d1c6ac7 (line 29)
inArray()load-s...d1c6ac7 (line 37)
[Break On This Error] jQuery('.sortable').sortable({});

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